A hybrid vehicle, in which an internal combustion engine, a motor generator, and an output shaft are connected to different rotation elements of a planetary gear unit and a ratio between a speed of the internal combustion engine and a rotational speed of the output shaft, that is, a transmission gear ratio is continuously varied by the planetary gear unit and the motor generator, has been known. As a drive system for such a hybrid vehicle, a system that includes two planetary gear units and a brake and realizes a continuously variable state, in which a transmission gear ratio is continuously varied by these components, and an overdrive state, in which a speed of an internal combustion engine is lower than a rotational speed of an output shaft, has been known (see Patent Literature 1). Other than the above, Patent Literature 2 is available as related art literature that is related to the invention.